Disposable articles and their manufacture from construction materials, including absorbent materials, woven and nonwoven fabrics, films, and adhesives, are described in a variety of United States patents, including Buell, U.S. Pat No. 3,860.003; Woon et al., U.S. Pat. No. 4,050,462; Strickland et al., U.S. Pat. No. 4,253,461; and Ryan et al., U.S. Pat. No. 4,326,528.
Disposable articles, such as diapers, are typically manufactured by combining a fluid-impervious film-backing sheet, absorbent materials and fibrous, fluid-permeable hydrophobic top-shelf. Such diapers typically also have an elastic band attached to the portion of the diaper forming a leg opening Such diapers additionally contain tabs for securing the article on the individual. The film-backing sheet provides a barrier preventing leakage of the article.
Such disposable articles are made in continuous processing by passing the materials of construction through high speed machines. In such continuous processing, components of the disposable article are continuously adhered to one another, and the disposable article is cut after assembly. Typically, the components are added to a polymer film in stages, including an addition of an elastic, an addition of a disposable, absorbent layer, and an optional addition of waist shields, attachment tabs, and other components. Any material added to the disposable article must have, as an essential property, ease of application at high construction application speeds.
Typical of such disposable articles are disposable infant diapers and disposable incontinent pads for adult patients. During the use of such disposable diapers and incontinent pads, disposable articles become wet and require replacement to ensure adequate humane care of the infant and adult patients. In the past, the wetness of the articles were monitored manually by either the visual or tactile inspection of the internal absorbent materials held within the impervious film-backing sheet. Such an inspection can be time consuming and often can be unpleasant.
In view of the nature of visual or tactile inspections of the disposable articles, development of moisture indicators that either change from colorless to colored or change from one color to another color in the presence of moisture were developed. Mroz et al., U.S. Pat. No. 4,231,370, discloses an aqueous latex or dispersion including a polymer adhesive-like material and an indicator in an aqueous base. A line of the Mroz materials are apparently spray-applied to the inside of the flexible film-backing sheet of the disposable articles. The indicator adheres to the polyethylene and dries to a flexible coating that is light yellow in color. The indicator, when wet during use, changes from a light yellow to a blue appearance.
The Colon et al. patents, U.S. Pat. Nos. 4,681,576, 4,743,238, and 4,895,567, teach wetness-indicating hot-melt adhesives which change in response to the presence of moisture based on a polyvinyl pyrrolidone, a polyvinyl pyrrolidone-vinyl acetate polymer, or an ethylene-acrylic acid polymer in combination with an organic acid and a wetness-indicating agent. The patents teach that the compositions can contain a variety of other ingredients, such as water-soluble waxes, glycerol esters, hydrogenated oils, and a variety of polymeric materials such ethylene-vinyl acetate copolymers, etc.
We have found that the aqueous latexes, such as those disclosed in Mroz et al., require increased manufacturing time to permit the evaporation of the aqueous portion of the latex. Such a requirement reduces the speed at which the disposable articles can be manufactured. We have also found that in typical formulations of hot-melt indicator material during manufacture the molten indicator can be phase unstable. Such phase instability can cause the indicator to be nonfunctional after application. While such phase instability can be remedied by introducing agitation into the hot-melt applicator machines, a need exists to formulate hot-melt indicator materials that are phase stable during manufacture and application.